Others point out that putting the fruit and vegetables in the trolley first is actually an inconvenience. The grapes are likely to get squashed by the bag of flour you buy later.

The bakery section often comes next: the smell of fresh bread has a special appeal.

This month there are also big stacks of Christmas biscuits, cakes, and confectioneries. These are bound to catch the eye, and again the supermarkets can say they are simply catering for the customer's changing demands.

But the shopper, faced with this bright and succulent heap of treasures, is again tempted to buy more than they might have planned.

In-store promotions also help delay the customer. The stall with the samples of free wine or delicacies is another temptation.

The longer shoppers spend in the supermarket, notes Damien Mather, a senior lecturer in marketing at Otago University, the more likely they are to buy.

The aim is to slow down the visit and distract the buyer. More time means more time for impulse-buying.

"There are no clocks in supermarkets," notes Lee.

The customer might have dashed in just to get bread and milk - but these "destination goods" are often placed at the back of the store.

Buyers have to pass a long line of temptations first.

The ends of the aisles are some of the most profitable parts of the supermarket.

"The shopper slows down to go around the corner," says Lee, and can't miss the big displays.

Some supermarkets are now cutting their aisles in two, just to provide more lucrative "gondola-ends". These spots are typically loaded with "treat items", says Consumer NZ deputy chief executive, David Naulls.

"You don't see a lot of displays of washing powder and detergent at the aisle-ends."

Supermarkets also make money by stacking their shelves in special ways.

They put the most profitable goods at eye-level, where the customer is most likely to see them.

In the cereals section, for instance, you will find there big- name brands of muesli and cornflakes that are big sellers and big money-makers.

The other stuff, like bulk bags of rolled oats, are on the lower shelves. So are the staples such as flour and sugar.

They know the customers will go looking for these drab but necessary items.

Manufacturers pay a "shelf allowance" to get a good spot on the shelves, says Guthrie.

The supermarkets will also use this prime real estate to feature their own-brand goods.

There are computer programmes which help the supermarket decide how much space each product will get, says Lee.

If supermarket selling techniques are both art and science, he says, shelf-stacking programmes are the science part of the equation.

Supermarkets take these calculations extremely seriously, just as they are serious about measuring the foot-traffic and noting your own grocery preferences when you swipe your loyalty card.

The better you know the customer, the more you can sell to them.

There is also a tendency to make own-brand colours and designs a little like the big-selling brands, says Lee.

A casual or confused customer might grab them thinking they are something else.

Customers tend to use the aisle around the outer wall as their main base, according to studies of the way shoppers navigate the store.

They then make shorter raids into the aisles. They don't merely go up and down each of the aisles in turn.

And on the outer ring of the store they will also see more of the gondola-ends.

Supermarkets tend to group their more tempting offerings, such as delicatessens and butcheries, along the outer wall where foot traffic is heavy.

Supermarkets point out, however, that this is also a matter of logistics. The butchery and the delicatessen require a "backstage" preparation area, says Lee. Deliveries are easier there too.

One piece of American research found that in supermarkets where customers enter on the right and then move anti-clockwise they spent an average of $2 more per trip.

Lighting tends to be bright in the supermarket, partly because "people associate 'bright' with 'clean'," says Guthrie. It also allows the prices and signs to be more easily seen.

Lighting, in fact, is another reason why fruit and vegetables are typically put near the doorway where there is more natural light.

In a wine shop, "you are pretending you know more than you do," so you might be lulled into more aspirational spending.

But would classical music help boost the profits in a South Auckland supermarket?

Guthrie says he doesn't think music is a major influence on supermarket shoppers, although it is "part of the mix".

The general approach in Kiwi supermarkets is to have bland "easy-listening" music that is pleasant, mildly stimulating but not soporific, and inoffensive.

"You're not going to hear heavy metal or rap."

Foodstuffs' Steve Bayliss says, "Music for us is ambient. It's about making customers feel relaxed during what can often be a mad rush to buy groceries and get home to cook dinner for the family.

"At the moment our New World stores are playing the 2013 Starship Christmas Album to create a festive mood."

UNHEALTHY PROMOTIONS

The critics say the supermarkets use their sophisticated selling techniques to sell unhealthy food as well as fruit and vegetables.

They say the supermarkets sell liquor at low prices and add to our binge-drinking culture.

They want the supermarkets to use their power for good, not just for profit.

"There is a simple clash between profit and health," says Professor Cliona Ni Mhurchu, programme leader for nutrition research at Auckland University's National Institute for Health Innovation.

The focus of the supermarkets, she says, is "to make a profit and clear stuff off their shelves".

They have sophisticated marketing techniques that help them do this, but this does not necessarily have healthy outcomes.

"What's available in supermarkets and what is heavily promoted," she says, "is not necessarily healthy."

While supermarkets might put fruit and vegetables at the front of their stores, she says, they also sometimes put alcohol.

The Newtown New World supermarket has been criticised for positioning its alcohol section just inside the door (fruit and vegetables come second).

The supermarket drew fire in 2010 from local residents and police.

And Liquor Licensing Authority chairman Judge Edward Unwin questioned whether, given its emphasis on the sale of liquor, it was a "bottle store which also sells groceries".

He gave the supermarket an 18-month liquor licence instead of the usual three-year one and asked it to produce a plan of how it would sell alcohol like a "good corporate citizen".

The supermarket is now under new ownership but did not respond to calls for comment.

It still has its alcohol section just inside the front door.

Ni Mhurchu says confectionery and sweets are often placed at important sites in the supermarket such as aisle-ends, promotional "bins' in the aisles, and at the checkout.

Bread and milk are placed at the back of the store and shoppers have to make their way through the "middle aisles" which feature biscuits, cakes, confectionery and sugary and processed drinks.

Ni Mhurchu and others are conducting a nationwide survey of supermarkets to measure the amount of shelf space given to different kinds of foods.

The study, which has been launched in Auckland and will be extended to include the whole country, will provide some "hard data" about the subject.

Bayliss says Foodtsuffs "recognises the important role it plays in encouraging Kiwis to eat healthy and balanced meals and take this responsibility seriously".

It has run a programme in schools since 2006 called Food for Thought which teaches students and parents about healthy eating, including nutritional information and label reading.

The layout of modern stores, he says, "means customers often have the choice of missing aisles if they wish such as confectionery".

Some items such as biscuits are located together "in a logical way to allow customers to easily find them rather than having to back- track, which we know is a common cause of frustration".

And from December 18, single alcohol areas will appear in Foodstuffs supermarkets as required by new alcohol legislation.

None of this satisfies the critics, of course.

Ni Mhurchu says New Zealand is lagging behind Britain, where 60 per cent of the food industry recently agreed to use "traffic light" nutritional labels on their food. Fast food restaurants had agreed to show the calorie content of their products on menu boards and to reduce calorie counts.

They had done this only because of government "leadership".

"The food industry hates regulation," Ni Mhurchu says. But they have agreed to voluntary changes to stave off the threat of government intervention.

This had damaged their commercial interests but has improved prospects for public health.

There is no sign that something similar would happen here, she says.

"The National Government obviously has a certain philosophy of individual choice," she says.

And so do the supermarkets.

"While we support healthy eating," says Mr Bayliss, "we are also mindful that our customers have the right to purchase and eat what they want."

WHERE THE POWER LIES

There are limits to how much power the supermarkets have, despite their great marketing skills.

Sometimes the consumers fight back.

There are few buyers, after all, who don't know that sweets and magazines choke the checkouts and threaten their wallets.

In response to consumer unhappiness, some supermarkets offer confectionery-free aisles. Again, we lag behind Britain, where some supermarkets have no sweets at any checkouts.

And sometimes the design of the maze misfires.

The Big Fresh group of supermarkets in the 1980s, notes Guthrie, made it difficult for customers to swap aisles. They were funnelled in one direction to the end.

And the Big Fresh attempt to make shopping a kind of entertainment also failed. It put statues of huge singing vegetables in its stores, partly to grab the attention of the kids.

But this was expensive and the customers seemed to dislike it.

When the Australian company Progressive Enterprises made its major move into the New Zealand supermarket trade in 2002, it soon targeted Big Fresh for death.

"It takes a lot of space and has a lot of gimmickry in it," Progressive managing director Ted van Arkel said.

Guthrie says most people "don't actually look forward" to visiting the supermarket, and they don't treat it as entertainment.

"They want something that works, they want it to be efficient, and they want to be out of there."

Likewise, the technique of putting the bread and the milk at the back of the store has also caused a backlash from some consumers.

Buyers who want to dash in and grab milk and bread and dash out are irritated at having to navigate the whole store.

So now some supermarkets put a small display of milk and bread near the entrance.

Guthrie questions how far the supermarkets are really able to manipulate their customers.

Impulse buying does not always mean buying something that you don't need.

If they see something in the shop and buy it, "it might be something they might not have remembered they were going to buy".

Lee suggests that this may be why some supermarkets regularly put toilet paper at the aisle-ends.

The supermarkets say they simply respond to the demands of their customers. They just help them find the stuff quickly and easily.

"And over the last few years we've updated our stores to reflect this demand, whether that's more and better promotions, more modern stores, wider aisles, clear signage, glass-topped freezers so people can see in, or clear discounts or promotions."

Consumer NZ's David Naulls questions this.

The whole strategy of the supermarket is, he says, "to try to encourage you to buy something you normally wouldn't."